Boris Johnson said how the Plymouth mass killer Jake Davison came to legally own a gun should be “properly investigated".
The Prime Minister described the 22-year-old's crane driver's shocking murder spree in the coastal city on Thursday as an “absolutely appalling” incident.
Davison killed five people, including his own mother Maxine and three-year-old girl Sophie Martyn and her father Lee, in a deadly six-minute attack, but Devon and Cornwall Police have said the firearm thatcops believe he used was owned legally.
Asked whether there should be a separate probe into how Davison came to be a licensed gun-holder, Mr Johnson said: "I think that without prejudging the investigation into what happened in Plymouth, what I can say at this stage is that my thoughts are very much with the families of all those who tragically lost their lives in an absolutely appalling incident.
"The point you is a valid one, but it needs to be properly investigated and gone into."
Pressed further on Davison's YouTube and Facebook posts in which the killer identifies with the "incel" movement - an online fringe group associated with misogyny and shootings in the US and Canada - the PM added: "This has just been drawn to my attention. I'm appalled by it, clearly, but I think this is something that will undoubtedly be part of the investigation."
Davison, 22, shot and killed his 51-year-old mother Maxine Davison, also known as Maxine Chapman, at a house in Biddick Drive in the Keyham area of the city on Thursday evening.
He then went outside into the street and shot dead Sophie Martyn, aged three, and her father Lee Martyn, aged 43, in an attack witnessed by horrified onlookers.
Davison moved along Biddick Drive, where he aimed and shot at two local residents – a man aged 33 and a 53-year-old woman – who are known to each other.
They suffered significant injuries not believed to be life-threatening.
He killed Stephen Washington, 59, in a nearby park, before shooting Kate Shepherd, 66, on Henderson Place. She later died at Derriford Hospital.
Devon and Cornwall Police received multiple calls about the incident at 6.11pm, with armed and unarmed officers arriving at the scene within six minutes and Davison found dead by 6.23pm.
Chief Constable Shaun Sawyer told Sky News that those present had faced “some of the most challenging scenes”.
“The first officers on scene encountered the child that had been shot in the street, with the adult, using what is described as a pump-action shotgun,” Mr Sawyer said.
“I won’t expand on that but most people can imagine what that was like for arriving officers. Further along Biddick Drive, we then have two injured members of the public as more officers arrive.
“And then, they’re pointing where Mr Davison has gone. Further officers are attending and then encountering a further murdered male and female and then ultimately Mr Davison himself who has taken his own life.”
It is believed that the mass shooting, which police are yet to establish a motive for, began with a “domestic-related incident” between Davison and his mother.
“We’ve never in my time had homicide followed by a rampaging firearms attack on random members of the public and then taking one’s life,” Mr Sawyer said.
“That is without precedent in my time as chief constable
